1. Field of the Invention
The present invention relates to positive feed tools, such as right-angle positive feed drills, and more particularly, to a method and apparatus for automatically moving a member away from a differential feed gear of the tool to cause a spindle of the tool to stop retracting.
2. Description of the Related Art
Positive feed tools, such as positive feed drills, are conventionally known for drilling holes in workpieces formed of substances such as steel, aluminum, titanium, and composites. Positive feed drills include a drill feed mechanism that feeds a drill bit into a workpiece.
FIG. 1 illustrates an example of a conventional positive feed drill, specifically a right-angle positive feed drill 10 that is coupled to a cutter 12. The positive feed drill 10 generally includes a spindle 28 that, in addition to rotating, advances a predetermined amount per revolution toward the workpiece to be drilled. Conventional applications for positive feed drills include, among other applications, drilling holes in various parts of aircraft.
The right-angle positive feed drill 10 includes an air motor 14. The air motor 14 is powered by a pressurized air source (not illustrated). As described below, the air motor 14 causes the spindle 28 to rotate. The spindle 28 is caused to rotate and feed by rotating the spindle drive gear 18 and spindle feed gear 20 with a differential feed gear 24 and differential drive gear 26. The spindle feed gear 20 includes internal threads that are threaded on the external threads 26 extending along the length of the spindle 28. Hence, when the spindle feed gear 20 is rotated in relation to the spindle 28, the spindle 28 will feed through the spindle feed gear 20. External threads 26 of the spindle 28 illustrated in FIG. 1 are left-handed threads. The spindle 28 also includes drive grooves 30 that extend along the length of the spindle 28. The spindle drive gear 18 includes internal male splines (not illustrated in FIG. 1) that engage with the drive grooves 30 on the spindle 28. Thus, when the spindle drive gear 18 is rotated, the spindle 28 also rotates.
When the air motor 14 is actuated, the spindle drive gear 18 is caused to rotate, which will turn the spindle 28 due to the engagement of the internal male splines with the drive grooves 30. In forward operation, or the drilling mode, the air motor 14 turns in a clockwise direction (as viewed from the rear of the tool 10), which turns a motor spindle 16. The series of gears 32, 34, 38, 40, 26 connect the motor spindle 16 with the spindle 28. More specifically, rotation of the motor spindle 16 will rotate the pinion 32, which in turn drives the gear 34, which is pinned or keyed to a shaft 36. The spur pinion 38 drives the idler gear 40, which drives the differential drive gear 26. In forward drill mode, the differential drive gear 26 is coupled to the differential feed gear 24 so that they turn in unison. The differential drive gear 26 is also engaged with the spindle drive gear 18. Because the spindle drive gear 18 is engaged with the spindle 28 via the drive grooves 30, the rotation of the differential drive gear 26 is transferred to the spindle 28. However, the spindle 28 is permitted to move longitudinally through the spindle drive gear 18 because of the drive grooves 30.
The spindle feed gear 20, which is threaded on the spindle 28, is driven by the differential feed gear 24 while in the forward position, as shown in FIG. 1. The spindle feed gear 20 threads the spindle 28 through the spindle drive gear 18 and feeds it toward the workpiece. Because a differential exists between the spindle drive gear 18 and the spindle feed gear 20, the spindle 28 is rotated and will advance toward the workpiece. The desired feed rate is obtained by the differential gear ratio between the spindle drive gear 18 and the spindle feed gear 20. In sum, when the air motor 14 is actuated, the spindle drive gear 18 rotates, which turns the spindle 28. When the spindle feed gear 20 is rotated faster than the spindle 28, the spindle 28 will feed, causing downward motion of the spindle 28. Conversely, when the spindle feed gear 20 rotates slower than the spindle 28, the spindle 28 will retract upward.
The right-angle positive feed drill 10 also includes a feed stop collar 42 and a feed engagement lever 44. At the completion of the advancement of the spindle 28, or at the completion of the drilling cycle, the feed stop collar 42 contacts the feed engagement lever 44. This contact lifts the differential feed gear 24 away from the differential drive gear 26 and locks it so that it does not rotate. Because the differential feed gear 24 is locked and is engaged with the spindle feed gear 20, the spindle feed gear 20 is also locked in a stationary position such that it does not rotate. With the spindle 28 continuing to rotate in a forward direction via rotation of the spindle drive gear 18, and the spindle feed gear 20 held stationary, the spindle 28 will retract.
As illustrated in FIG. 1, the cutter 12 includes a drill bit 45 for penetrating the surface of the workpiece to be drilled. A tool nose 46 surrounds the cutter 12, which attaches the tool to a drilling fixture offset from the workpiece to be drilled. The drill bit 45 is a tool that bores cylindrical holes.
As illustrated in FIG. 1, a retract stop collar 46 is attached to the spindle 28. After the spindle 28 has gone through a drilling cycle and the cutter 45 has drilled a hole in the workpiece, the spindle 28 is retracted. If the spindle 28 is permitted to retract completely, the retract stop collar 46 will abut against either the housing of the tool 10, or against another item in the tool, such as a gear, bearing, or bushing. That is, the spindle 28 will continue to retract until the motor is stopped or the retract stop collar 46 abuts against the drill and creates a high torque situation in the drive train of the tool. This high torque situation may cause damage to the internal components of the tool. For example, the spindle, gears, shafts, bearings or other portions of the drill may be damaged if the retract stop collar 46 is permitted to bear on the drill.
One conventional right-angle positive feed drill similar to that illustrated in FIG. 1 includes a valve that is actuated before the retract stop collar torques on the tool. With this conventional tool, when the retract stop collar actuates the valve, the motor of the tool is shut off so as to prevent the high torque situation and prevent damage. However, this approach of shutting down the air motor of the tool when the retract stop collar engages the housing of the tool is complicated and bulky, which makes it difficult for an operator to easily handle the conventional tool and perform maintenance on the tool. Because this conventional approach is bulky, the right-angle head of the drill includes stronger gears, shafts, and bearings, which further increases the size of the right-angle head.
With right-angle positive feed drills, it is particularly desirable that the right-angle head be as small as possible. This is because the drills are often used to bore holes as near as possible to the 90.degree. corner of L-shaped workpieces, which increases the strength of a subsequent connection formed through the drilled hole.
The larger the head of right-angle positive feed drills, the further the bore distance from the corner of the L-shaped workpiece. Thus, it is generally desirable in right-angle positive feed drills to increase the side-to-center distance SC (see FIG. 1), which is the distance from the side of the head to the center of the spindle. Reducing the head size of positive feed drills is also desirable because the drill may be handled easier during drilling.
Another conventional right-angle positive feed drill, similar to that illustrated in FIG. 1, approaches the problem of the retract stop collar torquing on the drill by including a clutch mechanism in the tool that will trip when the retract stop collar engages the housing of the tool during the retracting of the spindle. When the retract stop collar on the spindle engages the housing of the tool head, a torque load is placed on the spindle feed gear causing it to rotate. This, in turn, rotates the differential feed gear, which is ordinarily prevented from rotating during retraction of the spindle. Rotation of the differential feed gear causes rotation of a daisy wheel of the clutch. A pair of spring-loaded rollers are positioned in the housing of the conventional tool and are in engagement with a plurality of recesses in the daisy wheel. When the differential feed gear is caused to rotate during the retract mode of the tool because the retract stop collar abuts against the tool, the daisy wheel will also rotate, displacing the rollers against the force of the springs, similar to a racheting action. This approach is described in further detail in U.S. Pat. No. 4,592,681. With this conventional approach, the right-angle head of the positive feed tool is again complicated and bulky, which is problematic for the reasons set forth above. Additionally, rotation of the daisy wheel will repeatedly subject the spindle 28 to torque spikes when the spring-loaded rollers roll over detents of the daisy wheel, which will cause the stopped stop collar 46 to thread further on the spindle and possibly damage the drill. This conventional mechanism is also prone to wear due to the frictional engagement of the spring-loaded rollers.
Thus, it is apparent that some conventional positive feed drills are particularly vulnerable to being damaged when subjected to a high torque situation during retracting of the spindle. These positive feed drills may be permanently damaged if the operator of the drill does not immediately shut off the motor when the retract stop collar is about to abut against the housing of the tool during retracting of the spindle. Hence, an operator of conventional positive feed drills must continuously monitor the retracting of the tool to determine when the retract stop collar will engage the drill. Conventional attempts to address this problem are particularly complicated and bulky.
From the foregoing, it is apparent that the above-described constraints and problems associated with conventional positive feed tools has created a need for a new, compact, and simplified approach to preventing damage to the tool when the spindle of the tool fully retracts.